Changed out the headers on the '77. Had a pair of single wall pipes on her, provenance unknown, probably Mikes pipes. They had grayed and begun to rust over these years, discolored enough to where the old stock headers looked better. Stock muffs were cut off as they were rusted through and I figured that I'd use the exhaust adapters to mount the Commandos back on. The 1 3/8 OD X 1 1/2 ID were a good start, as the 1 3/8 OD slide right over the inner pipe of the stock headers, however, the 1 1/2 ID equals 1 5/8 OD which is the same OD as the Commandos.
The Fix.
I picked up some 1 1/2 OD straight exhaust pipe and cut two 1 1/2" sections. I trimmed the flanged end of the 1 3/8 X 1 1/2 ID down to 3/4" length past the start of the reduction, and inserted one of the 1 1/2 OD sections into it leaving 3/4's of an inch exposed to attach the muffler to. That left me with 3/4" of adapter that was exposed. Scrounging around, I found two muffler clamps that we're 3/4" wide, one for each side. I slipped the clamp on to cover the exposed section of the adapter and then put the muffler on with it's 3/4" clamp.
Pretty? A 1 1/2" clamp for both sides instead of two 3/4 inchers would be prettier but this worked and the price was right.